This invention relates to an optically addressable direct view display device and the method for producing a visible image with the display device.
Many different approaches to direct view display devices are known. One approach is to use a photochromic material in a display device to produce a direct view image. However, these devices are of relatively low optical sensitivity and require the use of thermal or in some cases visible radiation to erase the image and allow subsequent reuse.
The prior art also teaches the use of structural electrode arrays to produce electrochromic images in the form of characters and images. There is a one-to-one correspondence between the electrodes or activated electrode segment and the resulting image. This in general reduces the versatility of the device due to preconfiguration requirements and also presents certain difficulties in addressing and driving the display.
Another approach is to use a device with a photoconductive material overlaying an electrochromic material. The optical image reduces the resistance of the photoconductive material in the exposed area so that the corresponding area of the electrochromic material is energized by a voltage across the cell. This configuration solves the electrode problem of electrochromic devices but requires a more complex structure due to the layered structure. The materials must be selected for compatibility with all the other materials. Furthermore, the exposure and application of the voltage must be simultaneous unless a persistent photoconductor is used.
It is therefore a primary object of this invention to provide an improved direct view display device which is operable in response to low optical energy density.
It is a further object of this invention to provide a direct view display device which forms a latent image in response to optical energy which subsequently can be developed into a highly dense image.
It is another object of this invention to provide a direct view display device which can easily be erased and reused.
It is also an object of this invention to provide a method for producing a visible image by first producing a latent image in response to optical energy and developing the image into a highly dense image.
It is another object of this invention to provide materials suitable for use in the method.